1. Related Application
This application relies for priority on Korean application number 2005-06371, filed on Jan. 24, 2005, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.
2. Field of the Invention
The present invention relates to an image sensor and a method of forming the same and more particularly, to an image sensor including a buried barrier layer having a different thickness according to a wavelength of light and a method of forming the same.
3. Description of the Related Art
Image sensors convert optical images to electric signals. Image sensors are typically classified as complementary Metal-Oxide-Silicon (CMOS) image sensors or charge-coupled device (CCD) image sensors. The CCD image sensor has superior photo sensitivity and noise characteristics compared to the CMOS image sensor. However, it is difficult and complicated to highly integrate the CCD image sensor, and the CCD image sensor consumes a large amount electric power compared to the CMOS image senor. On the contrary, the CMOS image sensor is manufactured by a simpler manufacturing process compared to the CCD image sensor and the CMOS image sensor is suitable to be highly integrated. Also, the CMOS image sensor consumes less electric power than the CCD image sensor.
According to dramatic development of semiconductor manufacturing technology, a CMOS image sensor manufacturing technology has also rapidly developed, and characteristics of the CMOS image sensor have improved.
Conventionally, a pixel of the CMOS image sensor includes a plurality of photodiodes for receiving light and CMOS elements for controlling image signals inputted from the photodiodes. The photodiode generates an electron-hole pair according to wavelength and intensity of red, green, or blue light incident through color filters, and outputs signals varied according to a quantity of the generated electrons. That is, the CMOS image sensor detects images based on a variation of the signal outputted from the photodiodes.
The photodiode includes two impurity implantation regions doped with different impurities. Theses impurity implantation regions of the photodiode are formed to have identical range of projection (Rp). A penetration depth of light is varied according to the wavelength of the light. That is, higher wavelength of the light is penetrated deeper than shorter wavelength. However, an absorption coefficient in a silicon layer decreases in reverse proportion to the wavelength of the light. Since a red light has a longer wavelength than green light and blue light, the absorption coefficient of the red light is lower than the green and the blue light. Accordingly, the image sensor may have difficulty detecting the red signal and have unevenness of color detection ratio. The penetration depths of the green light and the blue light are limited within a photodiode region. Therefore, the photodiodes output stable image signals of the green and the blue light. However, since the wavelength of the red light is longer and the penetration depth of the red light is deeper, the red light may penetrate deeper than the photodiode region. Accordingly, if an electron-hole pair is generated outside of the photodiode region, the generated electron causes cross-talk since the generated electron moves to a photodiode region of a neighboring pixel.